Any fireplace positioned within the interior of a building requires some system for ventilating the combustion chamber of the fireplace where burning of fuel occurs. Generally, the combustion gases are collected and exhausted to the exterior of the building to avoid the gases accumulating in the interior of the building. Numerous ducting systems have been developed to collect and direct the combustion gases to the exterior of the building.
Some fireplace designs rely on the natural convection movement of heated air and combustion gases to establish and maintain a gas flow in the ducting system to the exterior of the building to properly ventilate the fireplace. In some cases, convection ventilation of a fireplace is not sufficient to permit safe and proper operation of a fireplace. In such cases, a fan unit is used to force increased air flow through the venting duct system to ensure appropriate ventilation.
There are, however, drawbacks to existing fireplace designs that used forced ventilation. When installing a fireplace, it is important that the fan unit be correctly sized to be able to force air through the length of vent duct system. On the other hand, the fan unit must not be so powerful as to over ventilate the combustion chamber such that heated interior air is drawn from the room through the combustion chamber and exhausted to the exterior resulting in heat loss and energy wastage. Fan units have to be sized to handle the largest conceivable ventilation flow rate for a fireplace depending on the rate of fuel combustion and therefore, there is a tendency for the fan units to over ventilate the combustion chamber leading to energy loss and wastage. Variable speed fan units can be installed to handle different ventilation rates but these units tend to be unreliable and expensive and add to the complexity of the fireplace unit.